refactor(server): rename Agent exception to Ai; add THREAD_NOT_FOUND / MESSAGE_NOT_FOUND codes (fixes 500s) (#19831)

## Summary

- The exception class under `ai-agent/` was serving every AI surface
(agent, chat, role, models, generate-text), so `Agent` was a misnomer.
Promoted to the `ai/` namespace; renamed `AgentException` →
`AiException`, `AgentExceptionCode` → `AiExceptionCode`, and related
interceptor / filter / handler / file names accordingly.
- Split the single `AGENT_NOT_FOUND` code into entity-specific codes.
Chat-thread lookups no longer reuse the agent identifier.
- **Fixes Sentry 500s on `GetChatMessages` / `chatThread`.** Every
"Thread not found" and "Queued message not found" throw site in ai-chat
was previously wired to `AGENT_EXECUTION_FAILED`, which maps to
`InternalServerError` (HTTP 500). They now use `THREAD_NOT_FOUND` /
`MESSAGE_NOT_FOUND`, both of which map to `NotFoundError` (HTTP 404) in
the GraphQL and REST handlers.

The underlying cause of *why* clients are asking for threads that no
longer resolve for them — per-user chat-thread create events being
broadcast workspace-wide — is addressed separately in a follow-up PR.

### Code map

- Added: `ai/ai.exception.ts`,
`ai/utils/ai-graphql-api-exception-handler.util.ts` (+ spec with new
THREAD/MESSAGE cases),
`ai/interceptors/ai-graphql-api-exception.interceptor.ts`,
`ai/filters/ai-api-exception.filter.ts`
- Deleted: `ai/ai-agent/agent.exception.ts`,
`ai/ai-agent/utils/agent-graphql-api-exception-handler.util.ts` (+
spec),
`ai/ai-agent/interceptors/agent-graphql-api-exception.interceptor.ts`,
`ai/ai-agent/filters/agent-api-exception.filter.ts`
- Updated: 21 call sites across ai-agent, ai-agent-execution,
ai-agent-role, ai-chat, ai-generate-text, ai-models, role, and
workspace-migration validators.

## Test plan

- [x] `npx nx typecheck twenty-server`
- [x] `npx jest ai-graphql-api-exception-handler` (3/3 including new
THREAD_NOT_FOUND and MESSAGE_NOT_FOUND cases)
- [x] `npx jest agent-role.service` (9/9)
- [x] `npx oxlint --type-aware` on all changed files (0 warnings/errors)
- [x] `npx prettier --check` on all changed files
- [ ] CI

packages/twenty-server/src/engine/metadata-modules/ai/ai-agent-execution/services/agent-actor-context.service.ts

@@ -5,9 +5,9 @@ import { type ActorMetadata } from 'twenty-shared/types';
 import { buildCreatedByFromFullNameMetadata } from 'src/engine/core-modules/actor/utils/build-created-by-from-full-name-metadata.util';
 import { UserWorkspaceService } from 'src/engine/core-modules/user-workspace/user-workspace.service';
 import {
-  AgentException,
-  AgentExceptionCode,
-} from 'src/engine/metadata-modules/ai/ai-agent/agent.exception';
+  AiException,
+  AiExceptionCode,
+} from 'src/engine/metadata-modules/ai/ai.exception';
 import { UserRoleService } from 'src/engine/metadata-modules/user-role/user-role.service';
 import { GlobalWorkspaceOrmManager } from 'src/engine/twenty-orm/global-workspace-datasource/global-workspace-orm.manager';
 import { buildSystemAuthContext } from 'src/engine/twenty-orm/utils/build-system-auth-context.util';
@@ -46,9 +46,9 @@ export class AgentActorContextService {
       await this.userWorkspaceService.findById(userWorkspaceId);
 
     if (!userWorkspace) {
-      throw new AgentException(
+      throw new AiException(
         'User workspace not found',
-        AgentExceptionCode.AGENT_EXECUTION_FAILED,
+        AiExceptionCode.AGENT_EXECUTION_FAILED,
       );
     }
 
@@ -72,9 +72,9 @@ export class AgentActorContextService {
       );
 
     if (!workspaceMember) {
-      throw new AgentException(
+      throw new AiException(
         'Workspace member not found for user',
-        AgentExceptionCode.AGENT_EXECUTION_FAILED,
+        AiExceptionCode.AGENT_EXECUTION_FAILED,
       );
     }
 
@@ -84,9 +84,9 @@ export class AgentActorContextService {
     });
 
     if (!roleId) {
-      throw new AgentException(
+      throw new AiException(
         'User role not found',
-        AgentExceptionCode.AGENT_EXECUTION_FAILED,
+        AiExceptionCode.AGENT_EXECUTION_FAILED,
       );
     }
 

packages/twenty-server/src/engine/metadata-modules/ai/ai-agent-execution/services/agent-async-executor.service.ts

@@ -23,9 +23,9 @@ import { countNativeWebSearchCallsFromSteps } from 'src/engine/metadata-modules/
 import { extractCacheCreationTokensFromSteps } from 'src/engine/metadata-modules/ai/ai-billing/utils/extract-cache-creation-tokens.util';
 import { mergeLanguageModelUsage } from 'src/engine/metadata-modules/ai/ai-billing/utils/merge-language-model-usage.util';
 import {
-  AgentException,
-  AgentExceptionCode,
-} from 'src/engine/metadata-modules/ai/ai-agent/agent.exception';
+  AiException,
+  AiExceptionCode,
+} from 'src/engine/metadata-modules/ai/ai.exception';
 import { AGENT_CONFIG } from 'src/engine/metadata-modules/ai/ai-agent/constants/agent-config.const';
 import { WORKFLOW_SYSTEM_PROMPTS } from 'src/engine/metadata-modules/ai/ai-agent/constants/agent-system-prompts.const';
 import { type AgentEntity } from 'src/engine/metadata-modules/ai/ai-agent/entities/agent.entity';
@@ -239,9 +239,9 @@ export class AgentAsyncExecutorService {
       });
 
       if (structuredResult.output == null) {
-        throw new AgentException(
+        throw new AiException(
           'Failed to generate structured output from execution results',
-          AgentExceptionCode.AGENT_EXECUTION_FAILED,
+          AiExceptionCode.AGENT_EXECUTION_FAILED,
         );
       }
 
@@ -255,12 +255,12 @@ export class AgentAsyncExecutorService {
         nativeWebSearchCallCount,
       };
     } catch (error) {
-      if (error instanceof AgentException) {
+      if (error instanceof AiException) {
         throw error;
       }
-      throw new AgentException(
+      throw new AiException(
         error instanceof Error ? error.message : 'Agent execution failed',
-        AgentExceptionCode.AGENT_EXECUTION_FAILED,
+        AiExceptionCode.AGENT_EXECUTION_FAILED,
       );
     }
   }